1. Field of the Invention
This invention relates to well tools, and more particularly to foot valves, especially such foot valves as may be used in pumping wells, for instance.
2. Description of Related Art
It has been common practice to use well pumps which are actuated by sucker rods moved up and down by a surface unit (pump jack, or the like), thus stroking the piston in the pump barrel to pump well liquids from the well. Such pumps commonly are seated in a pump seating nipple. The sucker rod string, being attached to the pump, is utilized in retrieving and re-running the pump for replacement or repairs.
Some wells may have sufficient surface pressure at times that the pump cannot be removed therefrom safely. Thus, it may be necessary to "kill" the well in order that the replacement operation may be carried out safely. It is desirable to have the ability to shut-in the well below the pump in order that the well pressure may be bled off, thus making it safe to open the well to the atmosphere before removing the pump. For this operation, a spring-loaded flapper valve has been used below the pump, and this valve has been held open by an extension or probe on the lower end of the pump which extends past the flapper valve when the pump is seated in its seating nipple. Upon lifting the pump a few inches, the flapper valve is allowed to close, after which the well pressure may be bled off. Great difficulties have arisen in pumping wells in this manner where such wells have steam injected thereinto at a temperature of about 600 degrees Fahrenheit (316 degrees Celsius). At such elevated temperature, the flapper valve spring has been unreliable, having a very short life. When the spring fails, the flapper valve will not move to closed position when the pump is lifted. This, then, creates a very expensive problem since it requires killing the well.
Flapper valves have been used on well packers for closing the bore therethrough upon withdrawal of the seal mandrel from its normal position in which it holds the flapper valve open. This is clearly disclosed in U.S. Pat. No. 2,189,703 which issued to Clarence E. Burt and Eugene Graham, Jr. on Feb. 6, 1940.
Applicant is aware of the just-mentioned U.S. Pat. No. 2,189,703 as well as U.S. Pat. Nos. 2,180,605 and 2,384,192.
U.S. Pat. No. 2,180,605 issued to Herbert C. Otis on Nov. 21, 1939 and discloses a plug (or closing tool) for plugging the lower end of a well tubing so that such tubing can be run into a well under pressure control. After the tubing has been run to depth, the tubing is pressured to move the plug from its seat and allowing it to drop to a bull plug below a plurality of perforations. Well fluids may then enter the tubing through such perforations and flow to the surface in the usual manner. Should it thereafter become necessary to remove the tubing from the well, a lifting tool is run into the tubing on a wire line or cable, the plug is engaged and lifted to its plugging position, pressure is bled from above it and the lifting tool disengaged therefrom, leaving the lower end of the tubing plugged.
U.S. Pat. No. 2,384,192 issued to Herbert C. Otis and John C. Luccous on Sept. 4, 1945. This patent shows a flapper valve like that of U.S. Pat. No. 2,189,703 and a plug (or closing tool) like that of U.S. Pat. No. 2,180,605.
None of the prior art with which applicant is familiar discloses a plug for use below a well pump, which plug is held in a non-plugging position when the pump is seated in its pump seating nipple and then is bodily lifted to its plugging position to plug the well below the pump when the pump is lifted from its pump seating nipple.
The device of the present invention is ideally suited to applications such as that described above.